1. Field of the Invention
This invention relates to an apparatus and a method for inspecting soldering condition of an inspected object, such as an electronic component soldered onto a substrate, and more particularly to an apparatus and a method for judging whether the soldering condition of the inspection object is acceptable on the basis of energy consumed by an inspection tool during the inspection where the inspection tool is depressed against a soldered portion of the inspection object and is subjected to high-frequency oscillation such as ultrasonic oscillation.
2. Prior Art
As a method of making a judgement whether a soldered portion of an electronic component on a substrate is acceptable or not, there is known a method of applying ultrasonic oscillation to the soldered portion to be inspected. FIG. 6 shows a side view showing a part of a soldering condition inspecting apparatus which is conventionally available. In the drawing, a depressing-type inspection tool 1 comprises a pin-like inspection piece 3 fixed to the distal end of a horn 2. This inspection tool 1 is substantially identical to a bonding tool used for an inner lead bonding apparatus disclosed, for example, in the Unexamined Japanese Patent application No. 4-199725/1992. An electronic component 5 has a plurality of leads 6--6 extending outward from the side surfaces thereof. Each of these leads 6--6 is bent downward and is soldered at its lower end onto an electrode 8 of a substrate 7 by solder 9. A base 21 mounts the substrate 7 thereon.
The inspection of soldering condition is carried out in the following manner. The horn 2 is subjected to ultrasonic oscillation generated by an appropriate ultrasonic oscillation means (not shown) which normally comprises an ultrasonic oscillator, a step-up transformer, and a piezoelectric element. Then, the lower end of inspection piece 3 is depressed on the upper surface of the lead 6, and provided an amplitude of a waveform of an ultrasonic current obtained to the inspection tool 1 by the ultrasonic oscillation means. The amplitude thus obtained is used to make a judgement on whether the soldering condition of the inspected component (i.e. the electronic component 5) is acceptable. In other words, this method is characterized in that the soldering condition is judged based on the correlation between bonding strength of the soldered portion and the amplitude of ultrasonic current of the ultrasonic oscillation means.
However, the value of an ultrasonic current is adversely affected by numerous factors, such as fluctuation of impedance of the inspection tool 1 and mechanical errors of the apparatus. In other words, these factors become the causes of measuring errors. Hence, accuracy cannot be assured in the judgement of the soldering condition; thus there may be errors in the judgement. It is believed that such fluctuation of impedance or mechanical errors chiefly result from the connecting rigidity between the horn 2 and the inspection piece 3 (namely, whether the connection of the inspection piece 3 to the horn 2 is rigid or soft) or scattering of sizes and materials of the horn 2 and the inspection piece 3. In this connection, the conventional method requires re-check of the characteristics of the ultrasonic current every time parts of the inspection piece 3 are exchanged, in order to newly set the judgement standard of the soldering condition. It therefore requires a great amount of manpower.